Oscillator



ay 10, 1938. o. M. OWSLEY OSCILLATOR Filed June 29, 1935 til PatentedMay 10, 1938 UNITED STATES PATENT OFF! C E OSCILLATOR tion of DelawareApplication June 29, 1935, SerialNo. 29,026

9 Claims.

"This invention relates to electron tube oscillators, particularly tooscillators operating on raw alternating current, .andhas special refer--enceto grid biasing arrangements for oscillators -of this general type.

Oscillators of the type described are useful in producing modulatedvoltages for aligning receiver equipment, calibrating frequency meters,and similar work where frequencies must be accurately and convenientlydetermined. They are also useful as radio beacons and for other purposeswhere an output of characteristic tone is required.

An object of the invention is to provide a. novel and useful gridbiasing arrangement for raw alternating current oscillators.

Another object of this invention is to maintain a negative potential onthe grid of an electron tube generator, operated on raw alternatingcurrent, throughoutthe entire A. C. cycle.

A more specific object of the invention is to obtain a negativepotential for the grid of a raw A. C. oscillator by a combination of twoindependently operating biases, to wit: self-bias by means of platecurrent drop in a cathode resistor during the positive plate currentcycle and an alternating current voltage of negative polarity bymeans ofa potential drop across an impedance, such as a transformer winding, andapplied through a grid resistor, during the negative half cycle of platecurrent.

Another and important object of the present invention is to ensureoptimum performance of a piezo-electric oscillator energized by raw a1-ternating current.

In order to make the invention more clearly understood there are shownin the accompanying drawing means for carrying the same into practicalefiect, without limiting the improvements in their useful applicationtothe particular embodiments, which, for purposes of explaining theinventive c0ncept, have been madethe subject of illustration.

Figure l is a circuit diagram of an electron tube oscillator,conveniently of the Hartley type, adapted to be energized by rawalternating current, and shows a grid biasing arrangement within thepresent invention.

Fig. 2 illustrates diagrammatically the grid biasing arrangement of theinvention as applied to a piezo-electric oscillator energized with alternating current.

Referring now to 'Fig. 1, the particular form of oscillator which hasbeen selected for illustration isa modified form of what is known as theHartley circuit. This oscillator comprises an electron discharge tube I,preferably but notnecessarily of the high vacuum thermionic type, havingthe usual grid, or control electrode 2 and a plate electrode fi. Thetube is also provided with a preferably indirectly heated cathode 4having afilamentary heaterB. The-tube and its associated circuits areadapted to be energized with "raw alternating current supplied from aconvenient source of, say, 110-120 volts-50450 cycles. The plate 5 isconnected through a plate coupling coilrfi and lead I to one terminal 8of the primary winding Tp of a transformer T which bridges the leads AC.from the'alternating current source, not shown. The filament 3 isenergized by ourrentinduced in the secondary winding Ts of thetransformer T.

The grid is connected by means of lead I 2, condenser l3, grid couplingcoil l4, and a short lead l2b toone terminal IU of the secondary windingTS, and by short lead [2a to the terminal 9 of the primary winding Tpopposite that (8) to which the plate lead I is connected.

Plate coil 6 and grid coil M are in energy transfer relation and areshunted by a variable condenser 15 which is provided for adjusting thefrequency of the oscillations generated by the tube I.

Inaccordance with the invention, two sources Ofgrid biasing potentialare provided. One of these, a grid resistor R1 is connected between thegrid 2 andone terminal ll of the transformer secondary winding Ts acrosswhich one of the discrete biasing potentials is actually developed. Theother grid biasingpotential is developed by a self-bias resistor R2,shown shunted by a condenser Cz'WhiChlS of suitable value to pass radiofrequency oscillations of the generated frequency. Resistor "R2 isconnected as by l2b to the terminal IU of the transformer winding Tsopposite that (ll) to which the grid resistorRi is connected. Thetransformer windings Tp-Ts are relatively so poled that the grid '2 "isprevented from'going positive irrespective of the instantaneous polarityof the alternating current applied, from the A. C. source, to the .anode5.

From the foregoing it will be apparent that the objectstof'the'invention are simply achieved by'a'pplying to 'thegridz an alternatingcurrent *VoItagein-phaSe with: that supplied to the plate 5 andadjusting the self-bias resistor R2 to such a value that "the negativebias generated thereby on the positive plate cycle exceeds the effectivepositive :bias developed .at that instant across TS R1 by an amount toensure proper operation of the device. Thus on the positive anodeonehalf cycle the grid is negative by the amount that the biasingvoltage generated by R2 exceeds the alternating current grid potential,and on the negative anode one-half cycle the grid automatically becomesnegative by the amount of bias developed across transformer secondarywinding Ts.

One advantage of the dual biasing arrangement, of the present invention,over single, socalled grid leak biasing systems, is that the effects ofgrid loading (caused by zero or positive bias on the negative plateswing) is substantially obviated, the device starts oscillating morereadily at the beginning of each positive plate swing ensuring asubstantially purely sinusoidal wave form; further, the efiiciency ofthe device generally is increased.

The dual biasing arrangement of the invention is especially useful instarting and maintaining the generation of oscillations when used inconnection with piezo-electric controlled oscillators energized by rawalternating current. This is so because a piezo electric element itselfrequires appreciable time to start oscillations, i. e., it is notinstantaneous in its operation. This reluctance or time lag is aproperty of the element per se and can be varied only to a small degreein the cutting of the element.

With 60 cycle power on the plate of the associated circuit there is only1/120th of a second available in which to build up positiveoscillations. With usual biasing arrangements, from the instant of zeroplate voltage and during the negative half cycle, there is zero bias onthe tube and high grid currents result. This results in grid loadingwhich must be overcome before the crystal can again start oscillating.By the time circuit conditions become normal, i. e., are in anelectrical condition to permit vibration of the crystal, so much time(of the 1/ 120th second plate pulse) has been consumed that the crystaldoes not have sufficient time to start oscillating before the platevoltage again falls to zero or some low voltage at which the circuitwill not oscillate.

The above and other disadvantages inherent with existing A. C. actuatedcrystal controlled oscillators are substantially obviated by the gridbiasing arrangement of the present invention.

To convert the circuit of Fig. 1 into a crystal v controlled oscillatorit is merely necessary to insert a crystal having the desired frequencycharacteristics and suitably mounted, in the grid circuit. Such anarrangement is shown in Fig. 2, which, with the exception of theaddition of the crystal and a novel frequency change-over device, issimilar in all respects to that illustrated in Fig. 1 and abovedescribed.

While the invention is not to be limited by the employment of a crystalof particular frequency response characteristic, it has been found,especially, when the oscillator is to be used for frequency calibrationpurposes, that there are certain definite advantages in employing acrystal cut in accordance with the principles set forth in copendingapplication Serial No. 29,000 to Charles Baldwin and Samuel Bokovoy,filed June 29, 1935, Patent No. 2,073,046, granted March 9, 1937. Suchcrystals are cut to oscillate at but two fundamental frequencies, one ofthe frequencies bearing a multiple or other predetermined usefulrelation to the other. Thus, in Fig. 2 the crystal P may be assumed tobe capable of oscillating at a Y-mode frequency of 100 kilocycles persecond and an X-mode frequency of 1000 kilocycles per second. Thecrystal is interposed between two electrode plates 33-3300 and, one ofwhich, 33, is connected to the grid 22 of tube 2| and the otherelectrode 330. is connected through a coil L21 to the filament at apoint 30 on one side of the secondary winding T5 of the transformer T.There are two plate coils, L22 and L23 which are adapted to beselectively coupled to coil L21 as by a switch S1. The mode or frequencyat which the crystal P oscillates is determined by the constants of thetuned circuit with which it is associated, thus, for 100 K. C.oscillation switch S1 is thrown to form a tuned circuit includingcondenser C22, coil L22 and all of L21. For 1000 K. C. oscillationswitch S1 is thrown in the opposite direction and a circuit tuned to1000 K. C. is formed by the combination of inductances L23 and a portionof L21, shunted by capacitor C25. The necessary connection between L23and L21 is provided by condenser C24, though it may be constituted bythe low impedance of the A. C. line. L22 and C23 now contribute littleto the constant of this tuned circuit because of the extremely highimpedance of these two units when in series.

As in Fig. 1, one of the dual biasing arrangements of the presentinvention comprises the transformer secondary winding Ts, to which gridresistor R21 is connected. The other grid biasing potential is developedby a self bias resistor R22, across which is shunted a condenser C22 ofsuitable value to pass radio frequency oscillations of the generatedfrequency. Resistor R22 is connected as by lead 32b to the terminal ofthe transformer secondary winding opposite that (3|) to which the gridresistor R21 is connected. As set forth in connection With Fig. 1, thetransformer windings are relatively so poled that the grid 22 is alwaysmaintained at a potential of a sign and intensity to ensure optimumperformance. Appropriate values to achieve the hereinafter describedoperating characteristics are designated upon the circuit diagram. Withcircuit constants of the values indicated, operation of the device ischaracterized by a high degree of overloading and distortion whereby asubstantial series of harmonics, particularly useful for calibrationpurposes, is obtained. Thus, assuming that the dial of a radio receiveris to be aligned, switch S1 is thrown to form a tuned circuit includingcapacitor C25, all of inductance L23 and a portion of L21, whereby thecrystal P will oscillate at its X-mode fundamental frequency, i. e. 1000K. C. The radio receiver is then tuned approximately to this frequencyand, when the A. C. note is heard in the speaker, the dial is calibratedat that particular setting. If the switch is then thrown to its otherposition the note will still be heard but it will be that produced bythe tenth harmonic of the 100 K. C. Y-mode fundamental frequency of thecrystal. The receiver dial is then slowly rotated and the note will fadeonly to reappear again at a dial setting corresponding to a frequency100 K. C. from the note first heard. It is thus possible to calibratethe dial exactly, as each multiple frequency is picked up by thereceiver.

Various modifications of the above described embodiments of theinvention will suggest themselves to those skilled in the art. Forinstance, if it is desired to operate the oscillator at a plate voltagehigher than that provided by a direct connection to the A. C. source,separate plate and filament transformer secondary windings may beemployed, in which case one terminal of the plate winding is preferablytied to a corresponding terminal of the filament winding-due regardbeing had to the phasing of the several windings.

Polyphase current may, of course, be utilized, if desired.

Although certain specific ways and means for accomplishing the objectsof the invention have been set forth, it will be understood that theyhave been given for purposes of explaining the inventive concept andshould, therefore, not be construed as limitations to the scope of theinvention.

What is claimed is:

1. In an oscillation generator, an electron discharge device having ananode, a cathode and a grid, a source of raw alternating current forsaid electrodes, and dual bias connections to said alternating currentsource for deriving therefrom a biasing voltage for maintaining saidgridat all times with respect to said cathode irrespective of theinstantaneous polarity of the alternating current supplied to saidanode.

2. The invention as set forth in claim 1 further characterized inthis,'that a piezo-electric element is provided intermediate said gridand cathode for controlling the frequency of the oscillations developedby said generator.

3. In an oscillation generator, an electron discharge device having acathode, a grid and an anode, a source of raw alternating current forsaid electrodes, and means including a grid resistor and a transformerconnected between said grid and cathode for deriving a negative biasingvoltage from said alternating current source for maintaining said gridnegative with respect to said cathode throughout the negative half cycleof the alternating current supplied to said anode.

4. In an oscillation generator, an electron discharge device having aheater type cathode, a filament for said cathode, a grid and an anode, asource of raw alternating current for said anode and said filament, anddual means operatively connected to said alternating current source andderiving a potential therefrom operative throughout both positive andnegative cycles of said alternating current to prevent said grid frombecoming positive with respect to said cathode.

5. In an oscillation generator, an electron discharge device having ananode, a cathode and a grid, a source of raw alternating current forsaid anode, two discrete sources. of biasing potential, and meansdetermined by the instantaneous polarity of the alternating currentapplied to said anode for successively impressing said biasingpotentials upon said grid to maintain it negative with respect to saidcathode.

6. In an oscillation generator, an electron discharge device having ananode, a cathode and a grid, a source of raw alternating current forsaid anode, means for deriving discrete biasing potentials from saidcurrent source and for'successively applying the same to said grid tomaintain it negative with respect to said cathode throughout the cycleof the alternating current applied to said anode.

'7. In an oscillation generator, an electron discharge device having acathode, a heater for said cathode, a grid and an anode, a tunablecircuit connected to said anode, a source of raw alternating current, atransformer having primary and secondary windings, circuit connectionsfrom said windings for impressing current from said source upon saidheater and upon said anode through at least a portion of said tunablecircuit, a self-bias resistor, a connection from said cathode throughsaid resistor to one terminal of said secondary winding, a grid resisterand a connection from said grid through said grid resistor to the otherterminal of said secondary winding, said transformer secondary windingbeing relatively so poled that said grid is maintained negative withrespect to said cathode throughout the cycle of the alternating currentapplied to said anode.

8. In an oscillation generator, an electron discharge device having acathode, a heater for said cathode, a grid and an anode, a source of rawalternating current, a transformer having primary and secondary windingsfor impressing current from said source upon said heater and said anode,a grid circuit connection between said grid and said transformer primaryand from said primary to one terminal of said secondary winding, aself-bias resistor, a connection from said cathode through said resistorto the terminal of said secondary winding to which said grid circuit isconnected, a grid resistor, and a connection from said grid through saidgrid resistor to the other terminal of said secondary winding, saidtransformer windings being relatively so poled that said grid isprevented from going positive with respect to the cathode irrespectiveof the instantaneous polarity of the current applied to the anode fromsaid source.

9. In an oscillation generator, an electron discharge device having aplate, a cathode and a grid, a source of raw alternating current forsaid plate, a circuit between said grid and said cathode, apiezo-electric element in said circuit, the electrical condition of saidcircuit during the brief period which includes the instant of zero platecurrent and the negative half cycle of said alternating plate currentbeing normally such as to inhibit optimum performance of saidpiezoelectric element, and dual means for deriving a negative bias forsaid grid from said alternating current source and operative throughoutsaid period to overcome said normal electrical condition of said circuitand including circuit connections for applying said bias between saidcathode and grid to thereby negatively bias said grid throughout saidbrief period.

OLLIE M. OWSLEY.

CERTIFI GATE OF C ORRECTI ON Patent No. 2,117,101. May 10, 19

OLLIE M OWSLEYL It is-hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: Page 5, first column, line 21, claiml, after the word "grid"insert negative; and that the said Letters Patent shouldbe read withthis correction therein that the same may conform to the record of thecase in the Patent Office.

Signed and sealed this 27th day of September, A. D. 1958.,

Henry Van Arsdale l) I Acting Commissioner 0f Patents.

